1. Field of the Invention
The present invention relates to a refractive index distributed optical element and an image sensor including the refractive index distributed optical element, and more particularly, to a refractive index distributed element having positive and negative refractive indexes varied within a plane and an image sensor including the refractive index distributed optical element.
2. Description of the Related Art
Up to now, in a projection display device such as a projector or a light receiving device such as an image sensor, an element that controls light direction and light spread is required for apparently improving the aperture ratio of pixels to convert the light direction.
First, a general configuration in the prior art in which the element that controls the light direction and the light spread is applied to a projector is described with reference to FIGS. 10A1 and 10A2.
In FIG. 10A1, a projector 800 includes a light source 801, a spatial light modulator 802, and a projection lens 803.
Light exiting from the projection lens 803 is projected on a screen 804 to display an image.
In the spatial light modulator 802, multiple pixels that modulate transmittance are arranged two-dimensionally.
FIG. 10A2 illustrates a cross-sectional view of peripheral portions of the pixels of the spatial light modulator 802.
The spatial light modulator 802 includes a microlens 812 on the exiting side, substrates 813 and 814, a liquid crystal layer 815, black matrixes 816, and a microlens 817 on the incident side.
Incident light 811 is deflected by the microlens 812 through an aperture between the black matrixes 816, and exits in a direction of the projection lens 803. The aperture ratio of the pixels is apparently improved by the microlenses 812 and 817 to convert the direction of light.
In the prior art, a configuration in which incident light is deflected by the aid of the decentering microlens 812 in order to deflect the light in the direction of the projection lens 803 as illustrated in FIGS. 10B1 to 10B4 has been proposed (for example, refer to Japanese Patent Application Laid-Open No. H06-180444).
A configuration in which light is deflected by the aid of a prism has also been proposed (not shown).
Next, a general configuration in the prior art in which the element that controls the light direction and the light spread are applied to an image sensor is described with reference to FIGS. 10B1 to 10B4.
FIG. 10B1 illustrates a general configuration of an area sensor 900 in which multiple image sensors are two-dimensionally arranged. Specifically, the area sensor 900 includes image sensors 901 such as CCDs or CMOS elements, which are two-dimensionally arranged.
FIG. 10B2 illustrates a lateral view of the area sensor 900 from in which light enters to the respective image sensors of the area sensor 900 from an exit pupil 912 of a camera lens.
Incident light 910 is light entering into central portions of the pixels of the area sensor 900, and incident light 911 is light entering into peripheral portions of the pixels of the area sensor 900.
The incident light 910 enters perpendicularly to a plane of the two-dimensionally arranged area sensor 900, and the incident light 911 enters obliquely to the plane of the two-dimensionally arranged area sensor 900.
FIG. 10B3 illustrates a cross-sectional view of the image sensors of the peripheral portions of the pixels of the area sensor 900 to which the incident light 911 enters.
The image sensors includes a microlens 920, an interlayer insulating film 921, a wiring layer or a light shielding film 922, and a semiconductor region 923 including an photoelectric conversion portion 924.
With the above-mentioned configuration, there arise such problems that the incident light 911 is not focused on the center of the photoelectric conversion portion 924, and the incident light 911 is scattered by the wiring layer 922 provided midway, and hence the incident light 911 may not be efficiently condensed on the photoelectric conversion portion 924.
For that reason, in the prior art, as illustrated in FIG. 10B4, the aperture ratio of the pixels is apparently improved to convert the light direction by the microlens 930.
That is, a configuration in which the position of the microlens 930 is shifted from the center of the photoelectric conversion portion 924 to the side of the central portions of the pixels so that the focal position is shifted to the photoelectric conversion portion 924 has been proposed (for example, refer to Japanese Patent Application Laid-Open No. H10-229180).
Further, a configuration in which a prism is used to deflect the oblique incident light to the photoelectric conversion portion side has been proposed.
However, the spatial light modulator and the image sensor in the above-mentioned prior art suffer from the following problems.
First, the spatial light modulator 802 illustrated in FIGS. 10A1 and 10A2 is described.
The incident light may be deflected to the projection lens 803 side by the aid of a decentering lens or a prism. However, the configuration of the spatial light modulator of the prior art illustrated in FIGS. 10A1 and 10A2 suffers from such a problem that alignment of the decentering lens or the like with the aperture is difficult.
The image sensors illustrated in FIGS. 10B1 to 10B4 are described below.
The incident light may be deflected to the photoelectric conversion portion side by the aid of the microlens 930. However, in the configuration of the image sensors illustrated in FIGS. 10B1 to 10B4, a beam diameter exited from the microlens 930 may not be converted into a narrower diameter. For that reason, the incident light hits on the wiring layer or the light shielding film 922 and is scattered.
Even if a prism is inserted, and the incident light is deflected to the photoelectric conversion portion side, the beam diameter is scattered without being converted.
The scattering amount depends on the position of the pixels of the area sensor and becomes larger as the pixel is more away from the central portions of the pixels.
For that reason, there arises such a problem that, in the peripheral portions of the pixels, the condensing rate of incident light is deteriorated, the scattering light arrives at the photoelectric conversion portion of the adjacent pixels, to thereby increase the mixture noise.
The deterioration in the condensing ratio and an increase in noise induce image deterioration.